This invention relates generally to a serial printer having a print head moveable across a print medium and more particularly to a serial dot-matrix printer. It is necessary in conventional dot-matrix printers to feed the sheet of print paper upon completion of one print cycle. Japanese Patent Publication No. 47-6528 discloses a head feed mechanism in the form of a helical cam having a reciprocating stroke. U.S. Pat. No. 4,250,808 shows a printer of the cycle-machine type. These prior art printers are designed in an attempt to achieve a small-size, and inexpensive printer construction. Some serial dot-matrix printers include, in addition to a head feed drive, a step motor or a plunger as a paper feed drive source for feeding the print paper at variable pitches to provide a graphics printing capability. A cycle-machine printer operates at all times in a mode equivalent to printing in a maximum allowable number of print positions, with the result that practical printing speed cannot be increased and the print paper cannot be fed at a fast speed or at different rates. A step motor or plunger for use as a paper feed driver has failed to provide a satisfactory small-size, inexpensive printer. Serial thermal printers incorporate a drive source such as for example a plunger for releasing the print head from the sheet of print paper when the latter is to be fed along. Such a printer however is complex in construction.
What is needed is a serial printer having a simple mechanism, small-size and low cost which is able to feed the print paper at variable pitches and at a fast rate. Also high speed printing capability is desirable.